The invention concerns of method directed towards the features in the preamble of the independent method claim and a device directed towards the features in the preamble of the independent device claim.
Polyvinylchloride (PVC) is used in a plurality of applications as insulation material for cables, as protective and decorating material, for pipe construction, in plastic compounds for floor coverings etc. To conserve natural resources and protect the environment, the recovery of plastic materials, including in particular PVC, has become more and more important. This is also increasingly the case for material compounds, such as electric cables whose additional components can also be recycled.
Various methods for processing electric cables having PVC insulation are known (DE 33 40 273 A1, DE 19 63 148). While the heavy fraction composed of different metal components can be separated relatively easily using physical methods due to the specific properties of the metals, the light fraction composed of different plastic components, such as PVC, PE (polyethylene), PP (polypropylene) etc. is difficult to separate by physical methods due to the plurality of different materials having similar physical properties. DE 44 41 229 C2 describes a method and a device for continuous processing of plastic coated cable remains and cable waste, wherein the metal core of the cable and also the PVC insulation material shall be recovered in pure form. This method is suited exclusively for separating PVC and metal. Other plastic insulation must be manually sorted in an expensive preparation station. Practice has further shown that, in the known system, the swelling PVC particles agglomerate to form a tough, thick sludge which precludes both separation of the PVC particles as well as desorption and recovery of the swelling agent.
As mentioned above, these recycling processes produce a plastic mixture, the light fraction of which contains further impurities, e.g. metallic remnants, sand, textiles and/or paper. Since, even with the addition of thermal stabilizers, PVC tends to thermally degrade when heated to more than 180xc2x0 C. thereby separating toxic chlorine and irritating hydrogen chloride, thermal utilization of the plastic mixture or cracking to obtain a crude oil-like basic material are not possible. Conversion of the plastic mixture into a plastic state and subsequent extrusion, which has to be effected at approximately 150xc2x0 C., is not possible, in particular when residual impurities of heavy metals such as copper are present since, at these temperatures, polychlorinated dioxins and furanes form under the catalytic influence of the heavy metals when a chlorine donator (PVC) is present.
According to prior art, the only processing options for such light fractions composed of different plastic materials is the so-called down-cycling into products of poor material quality, or disposal.
DE 41 06 812 A1 describes a method for the recycling of mixed plastic refuse, wherein layered plastic composites are disintegrated, the composite pieces decomposed into particles of a given material and the particles of differing materials subsequently separated into pure groups of a given material each. The disintegration of the composite pieces into particles of a given material is effected with mechanical shearing forces. The separation into pure groups of particles is effected by dispersing the particles in water and separating them in a plurality of hydrocyclone stages. Particularly for the case of plastic refuse containing PVC, same is disadvantageously poorly separable from other plastics of similar density despite the use of a plurality of hydrocyclone stages, since PVC, as is the case for most other plastics, does not swell in water and is therefore discharged in both the rising and sinking flow, even in the last hydrocyclone stage.
DE 2 900 666 A1 also discloses a method for separating mixed plastic refuse, wherein the refuse is disintegrated, suspended in a carrier liquid (water) and separated in sequential hydrocyclones. This method is also incapable of separating PVC from plastics of similar density.
DE 43 13 007 A1 discloses a method for separating a plastic from a support material. The plastic is separated from the support material through the use of a suitable solvent in which the plastic swells but the support material does not.
It is the underlying purpose of the invention to recover this PVC in pure form from plastic waste having a particularly high PVC content.
In accordance with the invention, this object is achieved by a method in that the soaked substance mixture is transported under pressure into an arrangement of at least two hydrocyclones which are connected in series. The first hydrocyclone separates a heavy fraction of impurities such as sand and metal particles and heavy plastic particles in the sink flow, and a light fraction of swelled PVC particles and light impurities and plastic particles in the rising flow. Subsequently, the pre-cleaned light fraction is sorted and the particle fraction comprising the swelled PVC particles and smaller plastic particles is fed to the second hydrocyclone in which the PVC particles are separated in the sink flow.
With respect to the hardware side of the system, the inventive object is achieved by a device, wherein the arrangement of devices for separating the swelled PVC comprises at least two sequential hydrocyclones and at least one sorter, disposed between the upper outlet of the first hydrocyclone and the second hydrocyclone, wherein at least one pressure transporter is disposed after the swelling container for soaking the PVC and the first hydrocyclone to transport the substance mixture.
Advantageous embodiments of the invention are characterized in the dependent claims whose features are explained in the description of the drawings.
The invention offers the substantial improvement that, after carrying out the steps explained below by means of a flow diagram, the PVC is present in pure form. The mixture consisting of further plastic components from which the PVC has been separated, can be further processed in a known fashion, e.g. thermally utilized, extruded or poured. The separated PVC has properties nearly identical to those of new material. Certain material properties, such as plasticity, flowability, tensile strength etc. of the PVC, which in its pure form is extremely brittle, can be influenced through the addition of softeners such as phthalic or terephthalic esters, alkylphosphates or phosphinoxides which partly dissolve in the swelling agent and/or solvent and are re-supplied to the PVC, separated from the other plastic materials. Advantageously, other impurities in the plastic mixture used such as metals, sand, textiles or paper are also separated from the PVC. The PVC thereby no longer contains, in particular, metallic remnants which would disturb further processing. An important feature of the inventive method is the constant shearing of the substance mixture and of the PVC enriched fractions successively separated therefrom in the simultaneous presence of the swelling agent thereby effecting constant core size reduction of the swelling particles while preventing their agglomeration.
The inventive device is sealed off in a gas-tight fashion such that swelling agent vapors cannot escape into the atmosphere but rather are almost completely recovered and recycled in the process. The swelling agent is preferably methylene chloride (dichloromethane, CH2Cl2) which effects rapid swelling of PVC without changing its chemical structure, while the other plastic components such as polyamides, polyadditions, polyolefines (PE, PP etc.) or PTFE do not or only slightly swell in this medium. The use of methylene chloride for separating PVC insulation from electric cables via mechanical agitation, such as vibrations, stirring, knocking or grinding effects is known per se from DE 23 28 448 A1.
The invention is explained in more detail below by means of a preferred embodiment and with reference to the drawing.